Tunable high-frequency push-pull power amplifier



Dec. 8, 1953 D. BOTERWEG ETAL 2,562,127

TUNABLE HIGH-FREQUENCY PUSH-PULL POWER AMPLIFIER Filed April 25, 1951 INVENTORS DIRK BOTERWEG SYTZE B REI ER ANDRIES GERRIT ROBEER AGENT Patented Dec. 8, 1953 TUNABLE HIGH-FREQUENCY PUSH-PULL POWER AMPLIFIER Dirk Boterweg, 'Sy'tze Breimer, and Andries Gerrit R'obeer, Hilversum, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, 001111., as trustee Application April25, 1951, Serial N 0. 222,77 8

Claims priority, application Netherlands May 9, 1950 '2 Claims. I

This invention relates to high-frequency pushpull power amplifiers comprising airor watercooled amplifying tubes with anode cylinders which are open at one end and comprising a lecher conductor as anode circuit. Power ainpliiying tubes, for example for powers of 10 kw. and higher are nearly always equipped with such anodes.

The present invention has for its object to provide a suitable construction for such an amplifier, which permits a wide wave length range to be covered with a high power (for example 100 kw.) at short wave lengths, down to approximately 10 meters, the losses being small.

According to the invention, the lecher conductor consists of two hollow conductors of fiattened cross-section at the sides facing each other and a short-circuit bridge arranged to be continuously displaceable between the flattened flanks and covering the whole width of the fiat sides, the open end of each anode cylinder being connected to the associated lecher conductor near one of the two long edges of the flattened flanks of the conductor, which flattened flanks extend substantially parallel to the axis of the amplifying tube. It is advisable that the short circuit bridge should occupy an oblique position relatively to the longitudinal direction of the lecher conductor such that the distance from the bridge to the anode cylinder along the said edge of the flattened .fiank of the lecher wire, which edge is connected to the open end of the anode cylinder is larger, and along the other edge is smaller in the case of a short-circuit bridge extending at right angles to the lon- 2 gitudinal direction of the lecher conductor. this manner the current distribution over the short-circuit bridge is more even, as will be explained later, as a result of which burning out of the contacts of the bridge is avoided.

It is advantageous to use a construction in which the lecher conductor consists of two equal circular conductors and the short-circuit bridge is secured to an arm rotatable about a shaft extending through the centres of curvature of the two conductors. In this event, preferably the innermost edges of the flattened lecher conductors are connected to the open ends of the associated anode cylinders, the short-circuit bridge being at an angle of less than 180 with the straight junction line to the axis of rotation.

For coupling the amplifier with a load, for example an aerial, use may be made of a cou pling loop in the form of. a second lecher wire. As will appear from the following, this loop is provided at that side of the anode lecher conductor, which is connected to the open ends of the anode cylinders.

.In order that the invention may be readily carried into efiect, an example will now be described in detail with reference to the accompanying drawing, in which the example is represented in perspective.

The lecher conductor constituting the anode circuit consists of two similar cylinder conductors I and '3 having flattened cross-sections at the adjacent sides. Owing to this form of its section, the 'lecher conductor has a high capacity and a low inductance per unit length and consequently a low surge resistance (for example 15052). This is desirable in order to prevent the electrode capacities of the amplifying tubes and other capacitors bridging the open end of the lecher conductor, from causing .an excessive reduction of the resonance frequency.

Between the flattened innermost sides or flanks of the conductors I and 3 (in the drawing the outermost flanks are also flattened but this is not essential), a short-circuit bridge 5 is displaceable, since it is secured to an insulating arm I which is rotatable about a shaft 9 extending through the centres or curvature of the curved conductors .l and 3. The short-circuit bridge 5 is provided at both sides with resilient contacts Hand l3 respectively jointly occupying the whole width of the facing flattened flanks of the conductors and 3, so that the considerable high-frequency circulating current, which in the case of a transmitter of 100 kw. may be of the order of 300 A, is distributed over a comparatively large number of contacts ll and 13 respectively, each of the contacts I I being connected to the opposite contact 5-3 through ashort metal strip 15.

.At one end, the lecher conductor 13 is permanently short-circuited by a plate or flange 111.. The free ends of the conductors I and 3 are connected respectively to the anodes of two water-cooled power amplifying tubes 21 and 23; each of kw. in this example. These tubes, of which only the foremost tube 2! is shown in detail in the drawing, are of conventional con struction and comprise an anode cylinder 25 which is open at the top 25 and surrounded for the greater part by a cooling water jacket 2? and a glass bulb 2 9 which is hermetically sealed to the anode cylinder 225 just below the open edge .25. Within the :bulb 29, the grid of the tube is secured to a chrome iron ring ti which is also sealed hermetically to the bulb and serves at the same time as a terminal for the grid. The end of a circular conductor 35 is electrically connected, through a broad metal strip 33, to the ring This conductor, together with a similar conductor 32 connected to the grid of tube 23, constitutes a lecher conductor of the same type as the conductor 3. The conductor 35, 3? acts as a grid oscillatory circuit and is tunable by means of a short-circuit bridge 4| rotatable about a shaft 38.

For the sake of clarity, only the foremost discharge tube is shown in detail, partly broken away, and the supports for the lecher conductors l, 3 and 35, 31 and for the shafts 5, 39 have been omitted in the drawing. Since the rear tube 23, as seen in the drawing, is entirely identical with the front tube 2 I, only the latter will be described in detail.

The anode and the jacket 21 are coaxially surrounded by a copper cylinder 43 which is open at both ends and furnished in the usual manner with inwardly bent anti-corona edges. Between the upper (open) ends of the anode cylinder 25 and the cylinder 53, or at least in the immediate proximity of those ends-an annular copper plate coaxial with the cylinders is provided, which plate establishes a connection of very low inductance between the cylinders 25 and 43 and may be screwed to a flange of the anode cylinder. The cylinder 53 has for its purpose to enclose the anode cylinder and accessories in a fieldless space to prevent corona phenomena along any comparatively sharp edges. At the same time the cylinder 53 and a cylindrical plate ll partly surrounding the cylinder 45 coaxially, constitute one of two neutrodyne condensers of the amplifier.

In order to prevent undue heating of the bulb 21 at the seal to the anode, which seal is located a few centimetres below the edge 25' of the anode cylinder, a metal cone i9 widening upwardly is provided just below the sealing edge at the outer side, which cone is also provided with an anticorona edge and has an open-worked shell. The sealing edge is provided in the fieldless space between the upper end 25 of the anode cylinder and the cone 55. The grid connection 3| may be provided with a similar cone.

The end of the lecher conductor I adjoins the cylinder 53 such that one of the two long edges of the flattened inner flank of the conductor, the innermost edge of the circular flattened strip, which flattened flank extends at least substantially parallel to the axis of the tube 2!, is connected to the open end of the anode cylinder 25.

In this construction, the inductance of the connection of the anode to the lecher conductor proves to be minimised which is of much importance for obtaining a wave range with a minimal wave length. The positioning of the tubes parallel to the flattened flanks is essential for constructional reasons, namely the saving in space, easy shielding of anode and grid space, and in View of the fact that in this manner the cylinder 43 and the corresponding cylinder associated with tube 23 electrically constitute an extension of the lecher conductor I, 3.

The connection between the lecher conductor I and the anode 25 passes over the annular plate 45 constituting a through-connection of low inductance. Alternatively, the lecher wire may be connected to the cooling water jacket 21. Owing to the skin effect, the high-frequency anode current passes exclusively along the surface 1. e. from the inner side of the anode over the open edge 25, through the apertured cone Q9, over the plate 45 and the anti-corona edge of the cylinder 43 to the upper edge of the conductor I and is then distributed over the flattened inner flank. The distance which the current has to travel to these contacts II of the short-circuit bridge 5, which are located nearest to the shaft 9, in the drawing the upper contacts II, is in general shorter than the distance from the other contacts II. To compensate for this difference, which would cause different current loads on the contacts II, it has proved important to give the short-circuit bridge 5 a slightly inclined position in the aforesaid manner. Thus, the distance from the bridge 5 to the anode 25 along the upper edge of the flattened inner flank of the circular conductor.I is greater, and along the other edge is smaller than in the case of a not inclined position of the bridge 5 or, in general, such that the distance from the bridge 5 to the anode 25 along that edge of the flattened inner flank, in the present case the innermost edge of the curved conductor I, which is connected to the open end 25 of the anode cylinder 25, is greater and along the other edge is smaller than in the case of a not inclined or radial-position of the bridge. Experimentally, an inclined position of the bridge 5 is obtainable such that all contacts II and I3 are loaded substantially to the same degree. This is of great importance to avoid trouble due to burning out of the contacts at very high current intensities.

For cooling the contacts II, three tubes 5I to 53 pass through the hollow lecher conductor I. Through these tubes cooling water flows, by which the anode 25 is also cooled, the tube 52 acting as a forward duct and the tubes 5! and 53 as return ducts. The conductor I may consist of three copper tubes 5i, 52, 53 interconnected by soldering flat flank strips to them.

What has been said with regard to the lecher conductor I naturally also holds for the conductor 3, which is a mirror image thereof, but otherwise is identical.

Instead cf being circular, the lecher conductor I, 3 may alternatively be differently shaped or straight, but in regard to cost and volume the first-mentioned construction is particularly advantageous and most suitable for applying the aforesaid constructional principles. As has been pointed out, the open end 25' of the anode cylinder in this construction is preferably connected to or near the innermost edges of the flattened flanks of the lecher conductors (I and 3). Structurally, this is the best solution, since the amplifying tubes 2| and 23 can then be arranged at a small height, with the grid and filament connections uppermost in the case or frame of the amplifier, the lecher conductors I, 3 and 35, 31 being entirely or partly housed in the upper part of the case.

For the transmission of output energy of the amplifier to a load circuit, for example an aerial. a coupling loop in the form of a separate, substantially semi-circular lecher wire 51, 59, is arranged substantially concentrically with the conductor I, 3. The wire 51, 59 extends along part of the conductor I, 5 and is terminated at one end by a fixed short-circuit bridge 6! located in the proximity of the amplifying tubes 2! and 23. The length of that part of the coupling loop 51, 59, SI which is coupled to the conductor I, 2 depends upon the momentary position of the short-circuit bridge 5 and, as appears from the drawing, is greater as the wave length adjusted is greater, which permits approximately the correct degree of coupling to be obtained. It is of importance for the coupling loop to be provided opposite that side of the conductor I, 3 which is connected to the open ends of the anode cylinders, in the present case at the inner side of the circular conductor 3. In fact, the current flowing in this conductor is, at least near the tubes 2! and 23, a maximum at this side of the conductor I, 3 so that at this point the closest coupling is obtainable, which is of particular importance with the shorter waves of the wave range.

Alternatively, the construction described may be used advantageously for air-cooled power amplifying tubes. In such tubes, the construction problems arising therein are, similarly to watercooling, for the greater part due to the large size of the component parts and can be solved satisfactorily in the aforesaid practical manner.

What we claim is:

17 A tunable high-frequency push-pull power amplifier comprising a pair of water-cooled anode tubes each having a cylindrical anode open at one end, and an anode circuit for said tubes including a lecher line having a pair of parallel hollow conductors extending longitudinally along a curved path, said conductors being of flattened cross section at the sides thereof facing each other, means connecting the ends of said conductors to the respective anodes, the flattened sides of said conductors being disposed in parallel relation to the axes of said cylindrical anodes, a short circuiting movable bridge occupying an oblique position relative to the longitudinal direction of said line interconnecting the flattened sides of said conductors over substantially the full width of said flattened sides and cooling channels extending through said hollow conductors to said tubes.

2. A tunable high-frequency push-pull poweramplifler comprising a pair of water-cooled anode tubes each having a cylindrical anode open at one end and surrounded by a water jacket, and an anode circuit for said tubes including a lecher line having a pair of parallel hollow conductors extending longitudinally along a circular path, said conductors being of flattened cross-section at the sides thereof facing each other, means connecting the ends of said conductors to the respective anodes, the flattened sides of said conductors being disposed in parallel relation to the axes of said cylindrical anodes, a short-circuiting bridge occuping an oblique position relative to the longitudinal direction of said line interconnecting the flattened sides of said conductors over substantially the full width thereof, means including an arm coupled to said bridge and pivoted at the center of curvature of said circular path for displacing said bridge along said conductors, and cooling channels extending through said conductors and communicating with said jackets.

DIRK BOTERWEG. SYTZE BREIMER. ANDRIES GERRIT ROBEER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,113,758 De Vries Apr. 12, 1938 2,138,181 Lindenblad Nov. 29, 1938 2,156,261 Evans May 2, 1939 2,370,423 Roberts Feb. 27, 1945 2,412,987 Hoffman Dec. 24, 1946 2,548,770 Caraway Apr. 10, 1951 FOREIGN PATENTS Number Country Date 604,652 Great Britain July 7, 1948 

